The invention relates to an opto-electronic coupler comprising an optical transmitter and an optical receiver which are secured to separate connection conductors and which are electrically connected to one or more further connection conductors via contact wires, the transmitter, the receiver, the contact wires and parts of the connection conductors being embedded in a primary enveloping body which is embedded in a secondary, non-transparent enveloping body. Opto-electronic couplers are used in, inter alia, protection systems for securing, for example, computers and telecommunications equipment against electric voltages from peripheral equipment. Said couplers are also used in audio and video equipment.
Such an opto-electronic coupler is known per se from European Patent Specification EP 192.634. The coupler described therein comprises a LED (light-emitting diode) as the optical transmitter and a light-sensitive diode as the optical receiver, which are optically coupled to each other via a primary, transparent enveloping body. The expression "transparent enveloping body" is to be understood to mean herein that the material of this enveloping body is optically transparent to optical signals emitted by the transmitter and received by the receiver during operation of the coupler. The wavelength of said signals may be in the visible light spectrum as well as in the UV and IR spectrums.
The primary, transparent envelope of the coupler is embedded in a secondary, non-transparent envelope. The latter envelope provides the coupler with the required mechanical strength and shields the primary enveloping body from external optical signals. In the known coupler, the surface of the primary enveloping body is treated in such a manner that the primary and secondary enveloping bodies are adhesively interconnected. This adhesion improvement is attained by treating the primary enveloping body with UV light, chemical reagents, corona or plasma discharges. By virtue thereof, the penetration of moisture into the interface between the two enveloping bodies is precluded. This penetrating moisture may cause a short-circuit between the connection conductors. A short-circuit occurs at electric voltages of the order of 5-10 kV or higher. In that case, an electrical conduction path is formed between the connection conductor(s) to which the transmitter and the receiver are connected. This conduction path is formed by the film of moisture which is present between the two enveloping bodies.
The known opto-electronic coupler has disadvantages. It has for example been found that in the manufacture of the above couplers the percentage of rejects is undesirably high. A considerable number of couplers in which the known adhesion-improving measure was used did not function at all.